So-called rotary vane feeders are known in general as metering apparatuses, with the aid of which bulk materials can be transferred out of an area at any pressure into a conveying line against a higher or lower pressure prevailing in the latter.
A cell wheel, seated in a rotationally fixed manner on a horizontal shaft, comprises a hub and radial vanes which, accordingly, bound wedge-shaped or trapezoidal chambers. The bulk material passes into at least one cell-wheel chamber, via a top charging opening, and after a rotation, for example through approximately 180.degree., is passed into a conveying line via a discharge opening, if appropriate, assisted by compressed air. It is usually the case that the quantity of bulk material which is metered in this way, first of all, rises as the rotational speed of the cell wheel increases and, as the rotational speed continues to increase, decreases again on account of the centrifugal force. Problems arise here in the case of sluggishly flowing, adhering and bridge-forming bulk materials since the relatively narrow inlet cross sections of the design hinder continuous filling of the cell-wheel chambers.
Furthermore, a mass flow, i.e., uniform discharge via the entire cross section of the storage container, is desired. If the material which is located in the center of the container is emptied more quickly than the material in the wall region, then incomplete emptying and regular filling of the storage container may result in the situation where it is only the material from the center of the container which is ever removed, and the material in the border region becomes old.
In order to achieve a high metering capacity even for sluggishly flowing bulk materials and to ensure the desired mass flow, the practice has thus been adopted, for example, German Offenlegungsschrift using a metering apparatus according to DE 34 25 895, of connecting to the cell wheel in a rotationally fixed manner a stirrer which extends upwards through the charging opening. This has improved the metering of sluggishly flowing bulk materials for certain metering capacities. In particular, in the case of a relatively low metering capacity, however, a stirrer of this type does not operate reliably.